The invention relates to a method of determining the qualitative composition of soil organic matter (SOM) of mineral soils using thermogravimetry. The method is straightforward and cost-effective, providing reliable figures for all mineral soils, regardless of climatic zones, geological base substrates, soil genesis, type of utilization, and other effects.
One of the most important features of mineral soils is the soil organic matter. The term xe2x80x9csoil organic matterxe2x80x9d encompasses any organic compound contained in soil, with the exception of living biomass. The SOM is composed of humus, dead vegetable and animal biomass, water-soluble organic compounds (e.g. carbohydrates, amino acids, microbial exoenzymes, lipides, vegetable and animal hormones, etc.), as well as other nonliving organic substances or organomineral components.
The term xe2x80x9chumusxe2x80x9d characteristics all those organic components of mineral soils, which accumulate during soil formation of soil genesis. They differ from all the other organic substances by their soil-specific character.
A wide variety of traditional methods, particularly of analyzed humidified SOM components, are known. They are intended to identify single components, using physical, chemical or biological procedures, so as to elucidate the relations between SOM and individual soil properties and, in particular, soil fertility.
In view of the ecological aspects in soil scientific research, there was an increasing orientation towards SOM components, easily degradable by microbes, with the aims of reducing ecological problems of industrial utilization of soil (e.g. pollution of water with plant nutrients), e.g. by reduced use of mineral fertilizers and optimized technological efforts (e.g. soil treatment), describing the behavior of soil pollutants, and analyzing other effects (e.g. acidification of forest soils). The humidified components of the SOM being relatively stable were deemed to be of minor importance in this context.
Similarly, the related development of methods for rating the quality of SOM components was directed to the identification of individual groups of substances or compounds having a direct relation to current local problems.
No information as to the general properties, function or behavior or SOM could be derived from these methods. For this reason, no methods are known to date which enable a generally applicable determination of the qualitative composition of SOM.
For example, DD 249 972 A1 and DD 252 890 A1 describe methods of determining the convertibility of the soil organic matter, wherein the sparingly mineralizable humic acids are removed, thus enabling the determination of readily mineralizable components of the SOM with high accuracy. In this way, an improved calculation of the annual nutrient liberation from the soil is possible. Relations to classification features of soils, to individual soil formation processes or properties of soils in separate climatic zones, to the functions of the soils within the biosphere. or to principles in the succession of ecological systems cannot be derived from the results of these methods.
DD 259 460 A1 includes a process which uses the varying significance of the thermal stability of humidified and non-humidified components to assess the biological availability and thus, the biological utilizability of convertible components. This process supplements methods for the quantitative determination of convertible components by a qualitative parameter, but is still limited to individual components of SOM and dependent processes of plant nutrient liberation.
Similar conclusions result from investigations on the thermal stability and biological degradability of plant substances (Siewert, C., Archiv Fxc3xcr Ackerxe2x80x94and Pflanzenbau und Bodenkunde, 1994, Vol. 38, pp. 179-193). The results suggest the suitability of thermogravimetry in the semi-quantitative detection of biologically convertible components and other features (e.g. hygroscopicity) in base materials of the soil organic matter. However, a transfer of these conclusions to the soil organic matter or to characterize the qualitative composition of the soil organic matter is not possible by means of the above-described procedure.
Numerous problems in current soil research arise from the absence of a generally applicable SOM quality assessment. To date, the presence of diverse classification systems with limited mutual compatibility impedes a worldwide comparison and an integrated interpretation of soil-related results, as well as description of the general functions of soils and, in particular, of the SOM in ecological systems.
It was therefore the object of the invention to provide a straightforward, cost-effective method of determining the quality of soil organic matter, which method could be used for mineral soils of all regions, climatic zones and types of utilization and would not require an expensive material identification of individual components of the SOM but rather, would be oriented on generally applicable, evolutionary principles of current soil formation.
It has been found that the object of the invention can be accomplished by means of a straightforward and cost-effective thermogravimetric method in accordance with claim 1.